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The Changing Definition Of 'Kilogram'
DrLudicrous writes "The NYTimes is reporting that the platinum-iridium standard mass for the kilogram is shedding at an appreciable rate -- at least compared to other reference masses. The Pt-Ir cylinder is kept in France, and measured annually, and the slight discrepancy is important because the kg is an SI base unit- thus other quantities such as the Volt are based on it. A new standard is being sought- the two frontrunners are counting the number of atoms in a perfectly spherical single crystal of silicon, and another technique uses a device known as the Watt balance."
Probably something to do with the varience of a flux capacitor.
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Gee, seems that nobody has anything particularly important to say about the topic of the post...virtually all the comments are off-topic.
I believe the difficulty of defining the kilogram is twofold. We traditionally measure mass as weight, the attraction of mass by gravity (usually the Earth's gravity). But it is difficult to measure either quantity precisely.
Mass is usually defined as the number of atoms of a given atomic weight, a difficult thing to measure accurately given the total number of atoms in a gram of any element. And due to the weakness of the gravitational force and its attraction over considerable distances it is one of the forces that has been difficult to measure as accurately as other forces, leaving the Gravitational Constant (G) as one of the physical constants defined to a relatively lower degree of accuracy than most other universal constants. The difficulty of measuring both these quantities accurately at the same time combine to make it difficult to define a precise standard mass.
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